Earthworm ID can be tricky. Many species show variability when it comes to their ID features, and this can make it difficult for recorders as they struggle to match their specimen with the image presented to them in their ID key. The tubercula pubertatis (TP) of one Lumbricus rubellus may look the same as the other examples of this species from the same site but appear different on specimens of the same species from a different site. And the widely paired setae of Octolasion cyaneum look very different from the widely paired setae of Dendrobaena veneta.
This can knock the confidence that recorders have in their determinations, but it’s understandable that printed publications like the Key to the Earthworms of the UK & Ireland (2019) Sherlock, E. can’t include a huge number of photographs without driving the size and cost of the publication upwards.
So, I decided to team up with fellow ESB Tutor Kerry Calloway to undertake a project to build a library of photographs of earthworms and their ID features that can be accessed online by recorders in order to assist them with their identifications. We gathered an earthworm collection from the teaching material that we use on ID courses and booked a slot to use the photography equipment in the Angela Marmont Centre at the Natural History Museum. Both Kerry and I are fairly inexperienced when it comes to photography, but we soon got in a rhythm and we photographed our first 6 species.
Our aim for each species was to get a range of images for each species, including images of:
The head to saddle region - this allows us to produce annotated images that show the segment numbers that the male pore, clitellum and TP all occur on
Head close up – Current ID keys only give close examples of a very small number of species to given token examples of epilobic and tanylobic heads. We wanted to include species-specific examples of each head type, including examples of tanylobic and epilobic heads for Dendrobaena veneta, which can have either.
Male pore close up – This is only used in the ID keys in a minor sense (one question asks if the male pore is on segment 15). However, the shape and size of the male pore does vary between species (and sometimes even within a species) so building a library of species-specific male pore images may be useful for recorders. Plus, it will help emphasise why people struggle to see the male pore on some Lumbricus species that have a very small one.
Clitellum close up – The TP, located on the clitellum, is probably the most important feature for earthworm ID as it is used to separate most species from one another. TP shape descriptions can be subjective, particularly when some specimens vary within a species.
Setae (tail end) close up – Like the two types of head, current ID keys just give token examples of widely-paired setae and closely-paired setae. Building a library of species-specific examples will allow recorders to compare what they see with a photographic example of setae spacing for the species they are considering.
Whole earthworm – Looking at the earthworm as a whole may not be an ID feature used in the key, but it can help recorders see if their species determination looks like the photographed example. Aporrectodea caliginosa and Aporrectodea nocturna have the same diagnostic features but the former is a medium-sized endogeic earthworm and the latter is a larger anecic earthworm. In this case it is only when you look at the earthworm as a whole (after establishing it is one of the two species) that you can reliably determine the species.
We’ve already undertaken our second photography session and are now working on editing the photos, so they can be used to create Species IdentiSheets and uploaded to a new Earthworm Identikit that is currently in development. Later this year we will release the first wave of Species IdentiSheets through the ESB website so watch this space…
Except where otherwise indicated, this work was created by Keiron Derek Brown on behalf of the Earthworm Society of Britain and is licensed under a Creative Commons Attribution 4.0 International License.